The present invention relates to an apparatus for controlling the tilt angle of a doctor blade.
In doctor blade applicators, the amount of coating mix applied to the web is controlled by adjusting the loading of the blade. However, changes in the degree of blade loading also cause a change in the blade's tilt angle, which complicates blade control.
In prior art doctoring units, the blade position has been manually adjusted as required. Compensation systems for blade tilt angle are also known. Finnish patent application 844035 discloses an apparatus in which two synchronously operated jacks are used to set the degree of blade loading. Finnish patent application 793164 discloses an apparatus in which loading control is effected by adjusting the shape of the blade while the blade supporting beam is stationary. In this case, the blade supporting beam incorporates a complicated control system for the adjustment of blade stiffness. In a system described in Finnish patent application 2203/74, loading control is achieved by rotating the blade frame about a shaft, thus causing a deformation of the blade shape and simultaneously altering the reaction force of the blade, while maintaining a constant blade tilt angle.
Manual blade control by methods of conventional technology is slow and incapable of complying with all loading conditions, which results in undesired deviations in the amount of coating mix applied. Compensation systems for doctor blade tilt angle deviations known in the art are complicated in structure, high in cost, and prone to malfunction. Also the control accuracy is often inadequate.
The aim of the present invention is to overcome the disadvantages associated with the aforedescribed prior art technology and achieve a totally new kind of apparatus for controlling the tilt angle of a doctor blade.
The present invention is based on designing a pivotally mounted structure of the doctor blade's supporting beam which abuts, via a lever arrangement, against the blade load adjusting device so that the rotation of the beam moves the beam closer to the web, thus increasing the blade loading, while the angle included by the blade tip and a tangent drawn to the contacting point of the tip is maintained constant or controlled in a desired manner.
The invention provides outstanding benefits.
The blade tilt angle controlling apparatus achieves, by means of an apparent adjustment (rotating the beam) of tilt angle, a change in the blade loading while the actual tip angle remains exactly constant, thus simplifying the adjustment of the coating mix application and additionally a better quality of the coating is achieved in transformation situations.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.